Surprise Symphony, byname of Symphony No. 94 in G Major, orchestral work by Austrian composer Joseph Haydn, so named for the “surprise”—a startlingly loud chord—that interrupts the otherwise soft and gentle flow of the second movement. The distinctive feature did not appear in the original score. Rather, it was added by the composer on a whim for the piece’s London premiere on March 23, 1792, and was retained in later performances.

For most of his career, which spanned primarily the second half of the 18th century, Haydn served as music director for the court of the Hungarian Esterházy family. With the death of Prince Miklós József Esterházy in 1790, Haydn was finally free to travel, and he set out for England, spurred by an invitation from Johann Peter Salomon, a German-born violinist and impresario, who presented six months of concerts in London each year. Knowing of the popularity of his Austrian friend’s works, Salomon was eager to present Haydn and his music in concert.

Haydn arrived in London on New Year’s Day, 1791, and remained in the city for a year and a half. Londoners turned out by the thousands to watch him conduct premieres of his new works, and critics and audiences alike were generous with their praise. In his diary entries during these tours, Haydn exulted in his local celebrity, the attendance at his concerts, the frequent dinner invitations, and the impressive concert receipts. He returned for a second 18-month visit in 1794–95.

Among the works heard at these concerts were 12 new symphonies, the last ones Haydn ever wrote, including the perennially popular Symphony No. 94 in G Major. The piece gained fame when the composer himself, while serving as conductor, impulsively altered the dynamics of the second movement. There has been much speculation on the reason behind the change. According to one account, Haydn had already given the downbeat to begin the movement when the gentle snores of a front-row patron piqued his sense of humour. He and his musicians forged ahead with the little theme until reaching its final chord, for which Haydn cued an immense fortissimo (loud tone), bringing the drowsy patron to his feet. Whatever Haydn’s motivation, the episode ultimately earned for the work its everlasting nickname, Surprise Symphony—in English. In German it is known as the symphonymit dem Paukenschlag—that is, “with the drum stroke,” an equally apt sobriquet.

Beyond such colourful anecdotes, the four-movement symphony follows a structure that was, at the time, still considered novel: it begins with a generally lively movement that offers several contrasting melodies; the second movement proceeds at a gentler pace, though with the moment of “surprise”; and the third movement is dance-flavoured, specifically resembling the then-popular minuet, a predecessor of the waltz. The last movement is the liveliest of all, with brisk and scurrying ideas that bring the piece to an energetic conclusion. Such a pattern became the norm for symphonies in the decades that followed, largely due to the initiative and stature of Haydn himself. He pioneered the structure, and his popularity was such that other composers, including Mozart and Beethoven, chose his work as their model for how a symphony should be composed.